[Sidefx-houdini-list] More time warp woes

gravatar at gravatonia.com gravatar at gravatonia.com
Thu Jan 8 09:07:26 EST 2009

Okies, having a little trouble with the expression for the delete sop for
solution 1.  I've tried what seems like to be the right expression and quite a
few variants after reading through the pstate help section.  A clue would be
appreciated.  Also, how would I reorder the points?  Never needed to do that
before.  While I wait to here from you I'll try to get solution 2 to work.


On Thu Jan  8  5:34 , Nicholas Pliatsikas <nick_p102 at hotmail.com> sent:

>Hi grav
>When your point count changes your timewarp freaks out due to the timeblend
using the point numbers to track and interpolate point positions. Particles use a
particle id attribute to tag and track particles in a simulation as point numbers
always change if your particle dies. For example you have 100 particles numbered
0 to 99 in the order they where born, but if your particle with a point number of
0 dies, the point number 0 needs to be filled by another particle which may be
the next particle in line i.e point number 1 becomes 0. So if the time blend
depends on this and your particles are randomly spread all over the place when
the point 0 dies, every other particle will shift its position to its tracked
point number position. I hope that makes sense.
>There is a few approaches to solves this. Number 1 is the easiest. Number 2 is
pretty tricky and suffers from floating point accuracy works arounds etc.
>1. On your popnet toggle off remove unused particles to keep dead particles, do
your retime etc using the timetools. Then delete the particles when the particle
state = dead. You may need to reorder the points based on particle id before hand
i cant recall. If you point count doesnt change the time bend and shift will work
fine by its self.
>2. For changing point orders make sure your popnet oversamples by 10 and save
out every 10 steps in your rop output driver (thats a 0.1 increment). You will
need to use an expression to drive the correct increment number in the saver due
floating point accuracy issues with $FF. I had some trouble getting this to be
consistant, as it would skip the odd frame when it got to over a few thousand
frames, but you may not have this issue. I think I ended up using a python
expression to obtain and use the correct sub frame increment.
>Then in your file Loader you can use the same expression as you did with the rop
driver to load in the correct increment)
>Heres the increment expression you can use, its the hscript one, i cant find the
python version tho.
>For the saver it would be. 
>floor($FF * (1 / ch("f3"))) * ch("f3")
>the result of this gets put into the filename where $F would be.
>on the file loader you will need will need two other parms.
>"targetFrame" is the frame you want to use. i.e the retimed frame number.
>and "inc", is how many steps where saved out i.e 10
>then this goes into another parm called "frameNumber"
>floor(ch("targetFrame") * (1 / ch("inc"))) * ch("inc")
>this also goes into the file name, where you would usually use $F. So all you
need todo is animate the targetFrame to retime as needed.
>There is a 3rd version i came up with which involved a mix of the increment
saver, loader and chops but this is so slow and heavy on memory with large point
counts it just isnt viable also its pretty complex.
>I hope some of this helps, as we had a nice bit of fun with this on the last
project we did. Its not nice at all!!
>> Date: Wed, 7 Jan 2009 22:45:42 -0500> From: sidefx at trinix.ca> To:
sidefx-houdini-list at sidefx.com> Subject: Re: [Sidefx-houdini-list] More time warp
woes> > Can you put your scene on the forum or send it to me so I can have a >
look. I'm curious about it.> > Also make sure all your time frame are set
properly on the cache node > and time blend.> > François> > Pablo Giménez wrote:>
> Mmmm not pretty sure here, but particles systems reuse the point index, $PT,> >
so maybe this is confising the time warp and time blend tools.> > I ma not sure
how well these tools work with geometry that is changing> > topology along the
animation> >> > 2009/1/7 gravatar at gravatonia.com>> >> > > >> Okies Folks,> >> I
am really getting frustrated with timewarp It works beautifully for> >> the> >>
first 150-200 frames then it totally flips out, inverting a twisting my> >>
particle> >> sim. I have tried applying it both to a bgeo sequence and a pop
merge and> >> it> >> does the same thing. As suggested, I am doing File or Pop
Merge -> Cache> >> ->> >> Timeblend -> TimeWarp. This did fix the problem with
timewarp skipping> >> frames> >> instead of interpelating them, but this sim
twisting is an even worse> >> problem.> >> Only other thing that I can think to
do is rebuilding my pop networks and> >> perhaps> >> even the force sop networks
they depend on, because they were originally> >> built in> >> Houdini 8. Has
anyone else had a problem like I am describing? Any> >> suggestions> >> other
that a network rebuild?> >>> >> Grav> >>> >> p.s. Where does the cache sop stash
what it is caching? Just curious.> >>
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